The present invention relates to novel polypeptides as for example obtainable from Neisseria meningitidis, to nucleotide sequences encoding such polypeptides, to the use of these in diagnostics, in therapeutic and prophylactic vaccines and in the design and/or screening of medicaments.
Neisseria meningitidis is a Gram-negative bacterium and the causative agent of meningococcal meningitis and septicemia. Its only known host is the human, and it may be carried asymptomatically by approximately 10% of the population (Caugant, D. et al, 1994, Journal of Clinical Microbiology, 32:323-30).
N. meningitidis may express a polysaccharide capsule, and this allows classification of the bacteria according to the nature of the capsule expressed. There are at least thirteen serogroups of N. meningitidis: A, B, C, 29-E, H, I, K, L, W135, X, Y and Z, of which serogroups A, B, and C cause 90% of meningococcal disease (Poolman, J. T. et al, 1995, Infectious Agents and Disease, 4:13-28). Vaccines directed against serogroups A and C are available, but the serogroup B capsular polysaccharide is poorly immunogenic and does not induce protection in humans.
Other membrane and extracellular components are therefore being examined for their suitability for inclusion in vaccines. Examples include the outer membrane proteins of classes 1, 2 and 3 (porins), and classes 4 (Rmp) and 5 (Opacity proteins). However, to date, none of these candidates is able to induce complete protection, particularly in children (Romero, J. D., 1994, Clinical Microbiology Review, 7:559-575; Poolman, J. T. et al, 1995, supra).
To create an effective vaccine, it is necessary to identify components of N. meningitidis which are present in a majority of strains, and which are capable of inducing a protective immune response (bactericidal antibodies). In this regard, reference may be made to Brodeur et al. (International Publication WO 96/29412) who disclose a 22 kDa surface protein which is highly conserved across 99% of all known strains of N. meningitidis. Injection of purified recombinant 22-kDa surface protein protected 80% of immunized mice against development of a lethal infection by N. meningitidis. Notwithstanding the discovery of this protein, there is still a need to isolate more surface proteins of N. meningitidis which are highly conserved across a plurality of strains, and which have immuno-protective profiles against N. meningitidis, and/or which may be used in combination with other components of N. meningitidis to enhance the efficacy of protection against this organism.
The present inventors have discovered a new gene which is present in all tested strains of N. meningitidis and which encodes a novel polypeptide having a predicted molecular weight of about 62 kDa. Based upon its sequence characteristics and homologies, this polypeptide is predicted to be an adhesin and this, together with experimental data suggests that it constitutes a surface protein which may be useful for the production of therapeutic and/or prophylactic vaccines against N. meningitidis as described hereinafter.
Accordingly, in one aspect of the invention, there is provided an isolated polypeptide or fragment thereof, or variant or derivative of these, said polypeptide selected from the group consisting of:
(a) a polypeptide according to SEQ ID NO 2;
(b) a polypeptide according to SEQ ID NO 5;
(c) a polypeptide according to SEQ ID NO 7;
(d) a polypeptide according to SEQ ID NO 9;
(e) a polypeptide according to SEQ ID NO 11;
(f) a polypeptide according to SEQ ID NO 13;
(g) a polypeptide according to SEQ ID NO 15;
(h) a polypeptide according to SEQ ID NO 17;
(i) a polypeptide according to SEQ ID NO 19; and
(j) a polypeptide according to SEQ ID NO 21.
Preferably, said polypeptide, fragment, variant or derivative elicits an immune response against one or more members selected from the group consisting of:
(i) N. meningitidis; 
(ii) said polypeptide;
(iii) said fragment;
(iv) said variant; and
(v) said derivative;
According to another aspect, the invention provides an isolated nucleic acid sequence encoding a polypeptide or fragment thereof, or variant or derivative of said fragment or polypeptide, according to the first-mentioned aspect. Suitably, said sequence is selected from the group consisting of:
(1) the nucleotide sequence of SEQ ID NO 1;
(2) the nucleotide sequence of SEQ ID NO 3;
(3) the nucleotide sequence of SEQ ID NO 4;
(4) the nucleotide sequence of SEQ ID NO 6;
(5) the nucleotide sequence of SEQ ID NO 8;
(6) the nucleotide sequence of SEQ ID NO 10;
(7) the nucleotide sequence of SEQ ID NO 12;
(8) the nucleotide sequence of SEQ ID NO 14;
(9) the nucleotide sequence of SEQ ID NO 16;
(10) the nucleotide sequence of SEQ ID NO 18;
(11) the nucleotide sequence of SEQ ID NO 20;
(12) a nucleotide sequence fragment of any one of SEQ ID NOS 1, 3, 4, 6, 8, 10, 12, 14, 16, 18 and 20; and
(13) a nucleotide sequence homologue of any of the foregoing sequences
Preferably, said sequences encode a product that elicits an immune response against one or more members selected from the group consisting of:
(i) N. meningitidis; 
(ii) said polypeptide of the first-mentioned aspect;
(iii) said fragment of said first-mentioned aspect;
(iv) said variant of said first-mentioned aspect; and
(v) said derivative of said first-mentioned aspect.
In yet another aspect, the invention resides in an expression vector comprising a nucleic acid sequence according to the second-mentioned aspect wherein said sequence is operably linked to transcriptional and translational regulatory nucleic acid.
In a further aspect, the invention provides a host cell containing an expression vector according to the third-mentioned aspect.
In yet a further aspect of the invention, there is provided a method of producing a recombinant polypeptide according to the first-mentioned aspect, said method comprising the steps of:
(A) culturing a host cell containing an expression vector according to the third-mentioned aspect such that said recombinant polypeptide is expressed from said nucleic acid; and
(B) isolating said recombinant polypeptide.
In a still further aspect, the invention provides an antibody or antibody fragment that binds to one or more members selected from the group consisting of:
(1) N. meningitidis; 
(2) said polypeptide of the first-mentioned aspect;
(3) said fragment of the first-mentioned aspect;
(4) said variant of the first-mentioned aspect; and
(5) said derivative of the first-mentioned aspect.
In yet another aspect, the invention provides a method of detecting N. meningitidis in a biological sample suspected of containing same, said method comprising the steps of:
(A) isolating the biological sample from a patient;
(B) mixing the above-mentioned antibody or antibody fragment with the biological sample to form a mixture; and
(C) detecting specifically bound antibody or bound antibody fragment in the mixture which indicates the presence of N. meningitidis. 
According to a further aspect, there is provided a method of detecting N. meningitidis bacteria in a biological sample suspected of containing said bacteria, said method comprising the steps of:
(I) isolating the biological sample from a patient;
(II) detecting a nucleic acid sequence according to the second-mentioned aspect in said sample which indicates the presence of said bacteria.
The invention further contemplates a method for diagnosing infection of patients by N. meningitidis, said method comprising the steps of:
(1) contacting a biological sample from a patient with a polypeptide, fragment, variant or derivative of the invention; and
(2) determining the presence or absence of a complex between said polypeptide, fragment, variant or derivative and N. meningitidis-specific antibodies in said sample, wherein the presence of said complex is indicative of said infection.
The invention also extends to the use of the polypeptide according to the first-mentioned aspect, the use of the nucleic acids according to the second-mentioned aspect or the use of the antibody or antibody fragment mentioned above in a kit for detecting N. meningitidis bacteria in a biological sample.
According to a further aspect of the invention, there is provided a pharmaceutical composition comprising an isolated polypeptide or fragment thereof, or a variant or derivative of these, according to the first mentioned aspect.
Preferably, said pharmaceutical composition is a vaccine.
In yet a further aspect, the invention provides a method of preventing infection of a patient by N. meningitidis, comprising the step of administrating a pharmaceutically effective amount of the above-mentioned vaccine.
In a further aspect, the invention provides a method of identifying an immunoreactive fragment of a polypeptide, variant or derivatives according to the first mentioned aspect, comprising the steps of:
(a) producing a fragment of said polypeptide, variant or derivative;
(b) administering said fragment to a mammal; and
(c) detecting an immune response in said mammal which response includes production of elements which specifically bind N. meningitidis and/or said polypeptide, variant or derivative, and/or a protective effect against N. meningitidis infection.